Collapsible cores are typically used in an injection molding apparatus for molding plastic parts requiring internal threads, undercuts, protrusions or cutouts or similar deformations which preclude the direct or straight line withdrawal of the molded plastic article from the mold cavity of the molding apparatus. Collapsible cores in molding apparatus permit the production of plastic parts in an economical, high or low volume basis.
There are a wide variety of collapsible cores in molding apparatus, such as for example, a molding apparatus with a positive collapse core as described in U.S. Pat. 4,456,214, issued June 26, 1984. The molding apparatus disclosed provides for a collapsible core with the core comprising separate, individual segments and with a mounting means for holding the segments against longitudinal movement and for providing a fixed pivot axis for the segments so that the segments may rock about an individual axis between a molding position and a release position, and with the core also comprising an actuator rocking the segments from one of said positions to the other. U.S. Pat. 3,618,170, issued Nov. 9, 1971, also describes a molding core employing collapsible and noncollapsible segments to provide for example a molded cap with an interrupted thread with the collapsing segments pivoting within a housing, while U.S. Pat. 1,274,673, issued Aug. 6, 1918, describes a glass molding apparatus with two pivoting, collapsible segments. These positive collapse cores employed in molding apparatus are all pivot-type collapsible cores.
An earlier collapsible core patent is U.S. Pat. 3,247,548, issued Apr. 26, 1966 hereby incorporated by reference. This earlier, basic collapsing core provided for a core having six wide and six narrow alternating segments herein all of which are collapsible and all of which are attached to a common core base. In this type of a collapsible core, the narrower collapsing segments are designed to collapse before the wider collapsible segments and thus provide a collapsible core with all segments collapsible with the narrow and wide collapsible segments collapsing at a different time in the molding cycle. While such a collapsible core in the molding apparatus is satisfactory, there are certain disadvantages associated with the use of all collapsible segments wherein certain segments must collapse in a timing sequence before other segments for the proper functioning of the collapsible core.
U.S. Pat. 4,130,264, issued Dec. 19, 1978, describes an expandable core for an injection molding apparatus with axially moving segments about a core pin having a plurality of faces with the faces sloping axially toward the axis of the pin and with a sleeve having first and second slides which alternate about the core pin with the slides also having a sloping surface. Such prior art collapsible-type core molding apparatus with so many segments are not well adapted to the production of very small plastic parts having internal undercuts, ribs, interrupted threads or similar deformations.